observations of new atmospheric electrical phenomena




Otha H. Vaughan,Jr. NASA/MSFC


Walter A. Lyons, FMA

Storm chasing with respect to tornados is quite the vogue these days,wears out one's car, burns up gasoline, and taxes the nerves of even the hardiest of the twister trackers.But there are other mysterious, thunderstorm-related phenomena that now can be viewed above distant thunderheads in he peace and tranquillity of a spring or summer night while observing the night sky from your location. Less than ten years ago, nobody had heard of sprites, blue jets and elves, in fact, the terms hadn't even entered the meteorological vocabulary. Recent research, however, has now confirmed that the observations, during the past century, by pilots and/or ground observers, who reported an entire menagerie of strange, luminous, lightning-related flashes dancing high above thunderstorm tops were occuring, can now be taken seriously. And you can, if you know how, observe some of these interesting phenomena with the naked eye. Here's a brief history of how sprites, jets, and elves were discovered using low light level TV cameras observing from the ground, aircraft, and space and how you might be able to spot some on your own.
In decades past, the textbooks said weather stopped at the tropopause, the layer separating the turbulent troposphere from the quiescent stratosphere above. Not so. As long ago as 1886, people were publishing reports in which they struggled to describe momentary discharges of "lightning," that they had observed to shoot upward and terminate high above storm clouds.

A 1903 paper by W.H. Everett discussed his observation
"rocket lightning ... a luminous tail ...shooting straight up ... rather faster than a rocket... "

An from Africa in 1937 came reports of D. Malan
"long and weak streamers of reddish hue...some 50 kilometers high..."

English and American scientific papers from the 1950s detailed what seemed to be flames appearing to shoot above thunderstorms seen near the horizon. Radar studies by G.C.Rumi of Cornell University in 1957 also reported that echos were being recieved from high in the stratosphere above thunderstorms that appeared to be from some form of lightning. Recently Earle Williams of the Massachusetts Institute of Technology took a closer look at a nighttime photograph of an Australian thunderstorm in his possession since the late-1980s which showed a lightning channel extending into the clear air above the storm top in turn appears to have "blue flame" fanning upward, perhaps even into the stratosphere. Pilots, both civilian and military, reported that they have seen at night faint plumes of light "extending from the top of the thunderhead from a pool of light from the lightning discharge ..." Many of these observations were published in books of meteorological esoterica alongside reports of turtles encased in hailstones, half meter wide snow flakes and showers of toads, chunks of ice, fish, seeds and whatnot. Interesting,but what could be the relevance of such events variously termed "upward lightning", "cloud-to-stratosphere lightning", "rocket lightning", or"cloud-to-space" lightning?

One clue was offered,as early as 1920 and then again in 1956, by Nobel Prize winning British physicist C.T.R. Wilson, the inventor of the Wilson Cloud Chamber, who saw "diffuse fan-shaped flashes of greenish color extending upward into the clear sky..." . He speculated then than such discharges between cloud tops and the ionosphere might be a normal accompaniment of lightning discharges to earth, but ones which are visible only under very special conditions. These might represent a heretofore unknown component of the global electrical circuit.

In 1980 Ron Williams, a pilot of a U-2 high altitude military recon aircraft, reported that he had seen in 1973, during a night flight while flying toward a typhoon in the Gulf of Tonkin, the top of a convective turret that was being illuminated from within by frequent lightning. When he was about 10 to 20 kilometers away, he was suprised to see a bright yellowish lightning discharge that came directly out the top of the turret and extended vertically upwards far above above his flight altitude of 20 kilometers. In 1989, by pure chance, University of Minnesota scientists John Winckler, Robert Franz and Robert Nemzek, while testing a low-light video camera for an upcomming high altitude scientific rocket shot, captured two fields of video showing giant twin pillars of light extending upward more than 30 kilometers above a distant thunderstorm.

With the hard evidence now in hand, the race was on in mainstream scientific circles to find out what was going on way up there.

Lightning researchers, Otha H. Vaughan, Jr. and Richard Blakeslee from the NASA Marshall Space Flight Center (MSFC ), Bernard Vonnegut, State University of New York at Albany (SUNY at Albany, and Marx Brook of New Mexico Inst. of Mining and Technology ( NMIT ) to at Socorro, N.M. began in 1986 to conduct from the Space Shuttle the Mesoscale Lightning Observational Experiment (MLE), to observe the earth's mesoscale thunderstorm complexs and to determine their flash rate and size of the lightning flashes being created by these systems with it's main purpose for providing design criteria for use in developing a future lightning detection and location satellite that would be placed in orbit during the 90's. During our observational program in October 1989 we observed strange 'upward lightning'like events or bolts of "rocket like lightning" in our video recordings of thunderstorms while using the low light level TV cameras of the Space Shuttle as the Shuttle was moving across Northwestern Australlia. The flashes were observed by payload bay Silicon Intensified (SIT) Vidicon cameras as they were observing,

at night, those thunderstorms that were located near the limb of the earth. The earth was being illuminated under very low moonlight conditions ( ie near new moon illumination ) thus enhancing the effective constrast ratio of the event against the earth's illumination. The evidence suggested that these flashes which did not look like the normal lightninmg must be occuring above the anvils of very active thunderstorm complexes which could not be seen in the video. Here's a few of the sprites that we have seen from the Space Shuttle as it orbits the earth. It is possible that we may see this type or similiar phenomena on other planets in the future as we fly by an observe these planets with low light level TV cameras and other sensors.

Now here's the rest of the story:

At FMA'S rural laboratory, the Yucca Ridge Field Station, situated near Fort Collins on the High Plains east of the Colorado Front Range, Dr. Walter A. Lyons and his associates, while conducting an lightning observational research program under a KSC Small Business Inovative Research (SBIR) NASA SBIR-92-1 contract that started in 1992 and was extended into 1993, waited during the summer nights of 1993 for the right conditions to be able to observe big thunderstorm clusters that were far enough away so they could easily be seen in the stratosphere and mesosphere region above their anvil canopies. This contract stated a research requirement "for a better understanding of risk, a characterization of upward travling discharges from the tops of electrified clouds and the frequency of occurance is needed ". The research goal was to try to determine if the upward appearing lightning might in some way present a hazzard to the Space Shuttle, if during a part of it's re-entry phase, enters the atmosphere and flys over an active large mesoscale convective storm system as well as to learn more about this newly observed phenomena.

On the night of 7 July 1993, giant thunderstorms were boiling over Kansas and Nebraska, one of the series of mesoscale convective complexes that drowned the midwest in record setting flooding rains far to the east.They aimed a low-light video camera, cousin to the night scopes used by the military,to the east and began taping. For the first two hours, not much happened, except for the almost continuous flashing of lightning within the distant clouds. Then, suddenly, a bright flash occurred high above the storm tops (appearing white on the monochrome television system screen). Over the next several hours, over 240 high altitude flashes were captured.

Here'a What a typical sprite looks like in from Dr. Lyons observational site.

The very next night, University of Alaska scientists, working under NASA HDQS and NSF funding , obtained similar images from a high-flying NASA DC-8 research aircraft over Iowa. Since then, thousands of flashes have been recorded using low-light video from the ground and from air. While easily visible on the television monitor on that very first night in Colorado, Dr. Lyons was unable to see anything with the naked eye while staring above the distant clouds. But several nights later, when the show started again, with some patience, and dark adapted eyes, there they were, he saw the bright reddish curtains dancing a gossamer ballet high above the distant storm clouds.

In 1994, while flying an extremely sensitive color camera normally used for auroral photography in a high altitude aircraft, the University of Alaska scientists confirmed that the flashes indeed have a generally reddish color, but which often fades to purple or blue in the downward extending tendrils.

These type flashes were named "Sprites" by Dr. Davis Sentman of UAF, which incidently are the creatures in Shakespeare's "The Tempest," in part because of their transient, ephemeral nature. But unlike the bard's characters, these sprites are very real indeed.

And the sprites were soon found to have company. At least two other distinct phenomena have been discovered to date. While flying near an especially active hailstorm in Arkansas, the University of Alaska team were startled to see blue beams of light shooting upward directly out of cloud tops at speeds over 100 kilometers a second.

They reach heights of 40 or 50 kilometers (two or three times the cloud heights) before fading away. Around 52 of these "blue jets" were seen that night during a 22 minute time interval. The Blue jets seems to be a very rare occurance at the present time since we have seen them only associated with one storm. The discovery of the blue jet appears to explain many of the strange reports over the last century that did not seem to jibe with the characteristics of the red sprites. It appears that the blue jet can be seen with the naked eye as reported by the pilots if you are lucky enough to be around on a dark night when that rare storm produces them. Based only on a few sparse reports, intense hailstorms may be the best candidates for the production of the blue jets but their origin is still unknown.

Before the discovery of the red sprites and blue jets there was an observation in 1990 of a flash in the airglow which was also observed using the Shuttle's low light level TV cameras as the shuttle was passing over French Guiana, South America and the cameras were looking, to the northeast with the coastline an Atlantic ocean in the field of view, at a thunderstorm in the distance rather that looking directly down to the earth as the cameras are usually used while conducting the MLE observational program. Dr.Bill Boeck, a NASA Summer Faculty Research Felow, who was working here at NASA MSFC,called it "Flash in the Air Glow"at that time. This type event can now be described as an Emissions of Light and VLF Perbations from EMP sources (ELVES) which were later recorded by others on video. In 1995 scientists from the University of Tohoku (Japan) and Stanford University, working with other science teams at the Yucca Ridge Field Station confirmed the presence of this phenomena and called it ELVES. These emissions were actually predicted by theorists before they were ever caught on tape. The elves appear as giant expanding disks of light between 70 and 100 kilometers altitude. They are caused by the passage through the ionosphere of the electromagnetic pulse (EMP), the intense radio waves emitted from powerful lightning flashes. Though huge, sometimes expanding to more than 400 kilometers in diameter, the elves are so transient (less than one-thousandth of a second), it is unlikely the human eye could detect them.

Here's a sample of a sequence of high speed video of what an ELF looks like as seen from a ground observing site located at the New Mexico Institite of Mining and Technology (NMIT) Langumire Laboratory, at Socorro, NM.

But the red sprites can be seen by the naked eye. They are by far the most common of these mesospheric creatures, and now we know where they "live". So a plan for some serious "sprite hunting" is relatively easy to develop.

Sprites come in a bewildering variety of sizes and shapes.They can look like giant red blobs, picket fences, upward branching carrots, or tentacled octopi. The sprite luminosity can extend upward as high as 95 km, with the brightest part usually located between 50 and 75 km altitude. The often bluish tendrils can sometimes extend downward below 30 km, close to, but probably not touching, the cloud tops. Sprites can occur singly or in clusters which sometimes fan out for over 150 kilometers. Sprites appear to be uniquely associated with cloud-to-ground (CG) flashes of positive polarity, usually those having peak currents larger than most of the other positive CG events in the storm. By comparison to the pencil- thin channel of their parent positive CG flash, the volume illuminated by a large sprite can reach hundreds or even thousands of cubic kilometers.

So now that we know about all the 'electrical action' above the clouds, a natural question is - can we see and photograph them? The answer is yes...and no. Taking standard photographs will not work unless you have a film with an ISO of 2 million (don't bother to ask for it in the photo store). To take images, you need a low-light video system. This is well within the reach of well funded scientific investigators, but not your a verage storm watcher. Yet under ideal viewing conditions you can indeed see sprites with the naked eye. Here's how.

Sprites occur high above very large thunderstorm systems. Since they are so high up, it is much easier to see them if they are at least 50 to 100 kilometers away. Sprites have been visually detected as far as 400 km out, but those occurrences are rare. Not every thunderstorm produces s prites, even if it has vigorous lightning. To improve your chances, check out the radar echoes on your local TV or the Weather Channel. Look for thunderstorm clusters that combined are at least 150 kilometers on a side. If you have access to data from the National Lighting Detection Network, look above the part of big storms where the positive CGs are occurring. This is most often in the large stratiform or anvil region of storm systems.

To actually view the sprites, find a location with a good view of the horizon. The further away from the city lights, the better. It is best to choose a dark night with no moonlight. In the eastern and southern United States, unfortunately, haze and air pollution can sometimes blot out the sprites. Let your eyes adapt to the dark for at least ten minutes. Look in the direction of the big storms. If you can see the illuminated tops of the distant storms, shield your eyes (a piece of cardboard can help) from the lightning flashing within the clouds. Concentrate your gaze at an altitude about four to five times the height of the cloud top, not the storm itself. Then be patient. In the more active storms, sprites can occur every one or two minutes, but every five to ten minutes is more common. They only last from one one-hundredth to one-tenth of a second. Blink and you can miss one. Due to a quirk in human night vision, you are often more likely to perceive them out of the corner of your eye. What will you see? To many it looks like the aurora borealis turning on and off in an instant. The true sprite color is salmon red, but at such low light levels the eye can play tricks on you and you might perceive them as green, orange or white. If you are looking in the right place and think you saw something, y ou probably did.

The best places in North America for sprite watching? Probably above the northern High Plains and upper midwest in a broad belt from Colorado to North Dakotas over to Minnesota, down into Texas, the mountains of New Mexico, or even Flordia. But they do occur above big storms worldwide, and have been spotted from aircraft and the Space Shuttle above Panama, Peru, Brazil, Africa, Australia and Indonesia, to name a few places.

The more scientists look above thunderstorms, the more they find. Researchers have been making measurements with satellites, spectro-meters, and photometers, and probing with radars and radio waves. It is clear that these progeny of thunderstorm lightning flashes can influence upper atmospheric electrical structure, radio transmissions, and perhaps the chemistry of the stratosphere and mesosphere. The mystery is just beginning to be unraveled. Theoreticians are just now furiously proposing and testing many mathematical models for sprites, jets and elves. Learned discussions abound in technical journals about electro-magnetic pulses, breakdown from quasi- electrostatic fields generated by massive shifts of hundreds of coulombs of charge within giant storm clouds, and runaway electrons accelerating to energies above a million electron volts in the intense electric fields above the storms. But for most of us, the sprite is a chance to spend a calm evening looking up at the night sky, or perhaps on the tailgate of a chase vehicle that never did quite catch the tornado, and just contemplate what's up there. And to wonder what else might nature be willing to tell us if we just keep looking very carefully, and we don't blink.